- Over the years, lead has been used as an additive in ceramic ware, paint, solder for plumbing, glass, and many other materials. As we began to understand just how dangerous lead was in human tissue, its use has drastically dropped. Some of the effects are miscarriages, kidney failer, slowing of nerve conduction, anemia, and inhibition of enzyme action. The glaze on ceramic dishes is no longer allowed to contain led. The problem is that many older dishes are still being used, and even new dishes containing lead may be imported from other countries.
- In this lab, you will test for the presence of lead leaching from ceramic ware. In selecting objects to be tested, older glazed items made before 1971 such as cups and bowls are likely suspects for lead. Also imported items, and brightly colored, worn down, or scratched items.
- You will prepare standards by quantitative methods, and use them as a comparison to the tests on the objects to get an estimated lead concentration.
MATERIALS:
Safety goggles
Containers for samples (film canisters are good for this)
Masking tape
White vinegar
0.5 M lead nitrate solution, Pb(NO3)3
1.0 M sodium sulfide, Na2S
Distilled water
9 or more 6 x 50 mm culture tubes
Rack for culture tubes
9 or more transfer pipets (eye droppers)PROCEDURE:
Collection of test samples.
1. Obtain several empty film canisters and put a piece of masking tape on the side of each for a label. Fill them with white vinegar to use in testing. Mark one canister with your name, and the words vinegar blank. This will be your untested vinegar sample.
2. Select the objects to be tested. Cover the surface of the item being tested with white distilled vinegar. Cover with a lid or plastic wrap to prevent evaporation. Allow the vinegar to stand at room temperature for 24 hours.
3. After 24 hours, pour the vinegar from each object into into a separate film canister and label with your name and the object tested. Secure the lid tightly.
Preparation of standards for sample comparison.
NOTE: we will be using transfer pipets to deliver accurate volumes. Always hold the pipete vertical and let gravity pull the drop off. This makes a very accurate small volume delivery. Always use a new pipete for each step.
4. Standard 1: Mark a 6 x 50 mm culture tube as standard 1, and place it in the rack. With a transfer pipet, add 20 drops of 0.5 M Pb(NO3)3 to the marked tube. The concentration (M) of lead for this tube is recorded for you in the data table. Now we need to find how many parts per million (ppm) of lead is in the tube.
- To convert molarity to parts per million (ppm). The molarity of the lead ion is the same as the molarity of the lead nitrate, Pb(NO3)3, because there is one lead ion in one molecule of lead nitrate.
- The concentration of 0.001M (1mM) in ppm is equal to the number of grams per mole (FW) of solute. Where M = molarity in moles per liter and FW = formula weight of solute in grams per mole (expressed as ppm per mole).
- The equation for standard 1 would then be:
0.5 M X 207.2 ppm
0.001 M= 103600 ppm 5. Standard 2: Mark a 6 x 50 mm culture tube as standard 2, and place it in the rack. Add 18 drops of distilled water to the second culture tube and add 2 drops of 0.5 M Pb(NO3)3 to this. What is the new concentration of the second tube? This can be calculated using the following relationship:
- Molarity 1 X Volume 1 = Molarity 2 X Volume 2
This is simply a cross multiplication problem, and can be rearranged to solve for Molarity 2 ( M2) as follows:
M 2 = (M 1) (V 1)
V 2M 2 = (0.5 M) (2 drops)
20 drops= 0.05 M
- Now calculate the ppm of lead for standard 2. Just plug your new molarity into the formula given in step 4. Record your answer in the data table.
6. Standard 3: Mark a 6 x 50 mm culture tube as standard 3, and place it in the rack. Add 10 drops of distilled water to the third culture tube and 10 drops of Pb(NO3)3 from the second culture tube. Using the formula given in step 5, calculate the molarity of lead for tube 3. Be careful to plug in the data correctly. Record the molarity in the data table. Calculate the ppm lead as before, and record in the data table.
7. Standard 4: Mark a 6 x 50 mm culture tube as standard 4, and place it in the rack. Add 18 drops of distilled water to the fourth culture tube and 2 drops of the Pb(NO3)3 from culture tube number three. Calculate the new molar concentration of lead, and ppm lead, and record on the data table.
8. Standard 5: Mark a 6 x 50 mm culture tube as standard 5, and place it in the rack. Add 10 drops of distilled water to the fifth culture tube and 10 drops of the Pb(NO3)3 from culture tube number four. Calculate the new molar concentration of lead, and ppm lead, and record on the data table.
9. Standard 6: Mark a 6 x 50 mm culture tube as standard 6, and place it in the rack. Add 18 drops of distilled water to the sixth culture tube and 2 drops of the Pb(NO3)3 from culture tube number five. Calculate the new molar concentration of lead, and ppm lead, and record on the data table.
10. Standard 7: Mark a 6 x 50 mm culture tube as standard 7, and place it in the rack. Add 10 drops of distilled water to the seventh culture tube and 10 drops of the Pb(NO3)3 from culture tube number six. Calculate the new molar concentration of lead, and ppm lead, and record on the data table.
11. Negative test blank: Mark a 6 x 50 mm culture tube as negative test blank (vinegar), and place it in the rack. Add 20 drops of distilled white vinegar to the culture tube. Both the molarity and ppm lead will be zero for this tube. Record on the data table.
Caution: The following steps should be done in a fume hood because small amounts of hydrogen sulfide gas is given off. Even a small exposure to hydrogen sulfide can cause nausea and headaches.
12. Add 2 drops of Na2S to each of the 8 culture tubes and record the color of the precipitate on the data table.
Testing your samples.
13. For each sample. Mark a 6 x 50 mm culture tube with the sample label, and place it in the rack. Add 20 drops of the sample from the film canister to the culture tube. Add 2 drops Na2S to the tube. Record the color of the precipitate in the data table. Compare the color of the tube to your standards, and determine the parts per million of lead found, if any, from the comparison.
- This test is not specific to lead, since other metals give dark, insoluble sulfides. However, lead is the most likely candidate. Assuming the color is due to lead sulfide, there is a rough correspondence between color and parts per million (ppm) lead concentrations.
DATA TABLE: Testing for lead. Test Tube Number Lead Concentration
(M)Color of Precipitate Parts per Million
of Lead (ppm)
Standard #1
0.5
103600
Standard #2
0.05
Standard #3
Standard #4
Standard #5
Standard #6
Standard #7
Vinegar
Sample #1
Sample #2
Sample #3
Sample #4
Sample #5
Back to Environmental Science Table of Contents
Back to Lab Dad's Laboratory
- In this lab, you will test for the presence of lead leaching from ceramic ware. In selecting objects to be tested, older glazed items made before 1971 such as cups and bowls are likely suspects for lead. Also imported items, and brightly colored, worn down, or scratched items.
TESTING CERAMIC DISHES
FOR LEAD
INTRODUCTION: